This invention relates to testing apparatus for dynamoelectric machines, and in particular, to a test system for automatically imposing fan loads on an electrical motor undergoing test. While the invention is described with regard to fan loads for electric motors, those skilled in the art will recognize the wider applicability of the inventive concepts disclosed hereinafter.
It has long been the practice in the manufacturing of dynamoelectric machines, and in particular, of electric motors, to run a series of operational and quality control checks to ensure that products produced by a motor plant, for example, are operating properly prior to shipment to a particular customer. Among the more common production tests imposed on motors during manufacture are a surge test in which a high voltage surge is applied to the motor windings to check for wire damage that can result in an open circuit of the motor winding; a high pot or high potential test to check the motor windings for electrical shorts between windings and to ground; and various start tests to ensure that the motor will start some predetermined load even under low voltage conditions.
With the growing concern over energy efficient products, motor manufacturers more recently have been required to ensure that their motors meet other performance standards prior to shipment. For example, many customers require that the motor be tested under operating conditions or load points to ensure that performance standards at such load point falls within predetermined, acceptable limits.
When motors are intended, in applicational use, to operate a fan load, for example, testing under full load has heretofore been troublesome for the motor manufacturer. In the first place, attachment of the fan load for the motor, when that load is a conventional fan blade, is relatively time-consuming and expensive because it is highly labor intensive. In addition, many of the fan blades used as motor loads are made from thin aluminum sheets or other similar material which can be bent easily. The distortion of the pitch of a fan blade changes the operating conditions of the blade and motor combination so that it is difficult, under production conditions, to ensure that the fan blades themselves are calibrated properly.
The direction of rotation of a motor also requires verification in many instances. Again, with production volumes, it has heretofore been difficult to consistently check motor rotation, the historic test being a visual observation of the direction of rotation.
We have found that with relatively small motors, that is, subfractional motors, mechanical couplings between the motor and the device used to load the motor during test often adversely affects the motor test. With small motors, the effect of this coupling is unacceptable.
One of the objects of this invention is to provide a motor test system which facilitates testing of a motor under a desired load.
Another object of this invention is to provide a motor test system which automatically connects a fan load to a motor, and disassociates itself during test so that an accurate test at the desired load point is obtained.
Another object of this invention is to provide a simulated fan load which may be calibrated to a desired fan load which maintains its calibration over extended time periods.
Another object of this invention is to provide a simulated fan load which facilitates the automatic determination both of motor speed and direction of motor rotation.
Another object of this invention is to provide a test device for determining speed and direction, particularly of relatively small motors, which imposes absolutely no load on the motor during test.
Another object of this invention is to provide a low cost device for conducting a predetermined number of motor tests.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.